Measurements of two photon excitation spectra for photolysis of various caging groups are being carried out to define those that uncage the most efficiently with currently available laser systems. Released molecules (typically the neurotransmitters glutamate and GABA) are detected by standard HPLC analysis or by fluorescence quantification (if a caged fluorophore is available using the caging group under study) . In our initial work the caging groups 4,5-dimethyloxy-2-nitrobenzyl ester (DMNB) and (a-2-carboxy)-2-nitrobenzyl (CNB) were characterized using CNB caged g-aminobutyric acid (CNB-GABA) for measurements of the properties of the CNB caging group, and DMNB caged fluorescein as a representative compound for the DMNB group.